How to add a checkbox to a pie menu?
The boolProperty needs to be registered to a particular type.  In the example below I've associated it with a camera (data) type.

bpy.types.Camera.xxx = BoolProperty()


To assign a property to an Object type would use

bpy.types.Object.xxxx = BoolProperty()


Then all objects in the blend file will have the xxxx property.  Use bpy.types.Scene for scenes.. etc.

I used code from https://blender.stackexchange.com/a/40793/15543 for the keymap, it's mapped to Alt-E

Restrict bl_idnames to lowercase, no spaces, only one period . for example "object_mode.xxxx_yyyy" not "Object Mode.xxxx_yyyy"

import bpy
from bpy.types import Menu

from bpy.props import BoolProperty

class VIEW3D_PIE_template(Menu):
    # label is displayed at the center of the pie menu.
    bl_label = "Macbook_Controller"
    bl_idname = "object_mode.mc_pie_menu"

    def draw(self, context):
        layout = self.layout
        # get the camera, use a poll method to check no cam
        scene = context.scene
        camera = scene.camera.data
        pie = layout.menu_pie()

        pie.prop(camera, "iSight_Camera_Indicator", text="iSight Camera Indicator Toggle")

def register():
    # register the property to a camera (data) type
    bpy.types.Camera.iSight_Camera_Indicator = BoolProperty(
                    name = "iSight Camera Indicator Toggle",
                    description = "Turns the iSight Camera Indicator ON and OFF",
                    default = False
                                            )
    bpy.utils.register_class(VIEW3D_PIE_template)

    wm = bpy.context.window_manager
    km = wm.keyconfigs.addon.keymaps.new(name = "Window",space_type='EMPTY', region_type='WINDOW')
    kmi = km.keymap_items.new("wm.call_menu_pie", type = "E", alt=True, value = "PRESS")
    kmi.properties.name = "object_mode.mc_pie_menu"

def unregister():
    bpy.utils.unregister_class(VIEW3D_PIE_template)


if __name__ == "__main__":
    register()
    bpy.ops.wm.call_menu_pie(name="object_mode.mc_pie_menu")